<!DOCTYPE html>
<html lang="en">
<head>
  <meta charset="UTF-8">
  <title>Title</title>
</head>
<body>
<button id="hd">后盾人</button>

</body>
<script>
  <!--   简单理解，回调函数就是在其他函数中执行的函数 -->
  let button = document.getElementById("hd");
  button.addEventListener('click', function () {
    alert(this.innerHTML)
  })

  let hd = [1, 2, 3, 4]

  hd = hd.map(i => i += 10)
  console.log(hd)

</script>
</html>